Okay, so back in a time called World War II, two big countries called Poland and the Soviet Union were fighting together against another big country called Germany. But when the war ended, everybody tried to get back to their own countries and live in peace.
Unfortunately, the Soviet Union decided they wanted a bit more land and power, so they took some areas in Poland and made them part of their own country. These areas were called annexed territories.
Now, Poland was not happy about this, because they felt like they should have been able to keep their own land. But the Soviet Union was very powerful and it was hard for Poland to do much about it.
So, some people who lived in those annexed territories were very sad because they felt like they were no longer part of Poland. They were now living in the Soviet Union and had to follow Soviet laws and rules instead of Polish ones.
Overall, it was a sad situation where one country took land from another country and made people unhappy. We hope that in the future countries can learn to work together peacefully and respect each other's borders.